Brain and abdominal temperatures at fatigue in rats exercising in the heat.
We measured brain and abdominal temperatures in eight male Sprague-Dawley rats (350-450 g) exercising voluntarily to a point of fatigue in two hot environments. Rats exercised, at the same time of the day, in three different trials, in random order: rest 23 degrees C, exercise 33 degrees C; rest 23 degrees C, exercise 38 degrees C; and rest 38 degrees C, exercise 38 degrees C. Running time to fatigue was 29.4 +/- 5.9 (SD), 22.1 +/- 3.7, and 14.3 +/- 2.9 min for the three trials, respectively. Abdominal temperatures, measured with intraperitoneal radiotelemeters, at fatigue in the three trials (39.9 +/- 0.3, 39.9 +/- 0.3, and 39.8 +/- 0.3 degrees C, respectively) were not significantly different from each other. Corresponding brain temperatures, measured with thermocouples in the hypothalamic region (40.2 +/- 0.4, 40.2 +/- 0.4, and 40.1 +/- 0.4 degrees C), also did not differ. Our results are consistent with the concept that there is a critical level of body temperature beyond which animals will not continue to exercise voluntarily in the heat. Also, in our study, brain temperature was higher than abdominal temperature throughout exercise; that is, selective brain cooling did not occur when body temperature was below the level limiting exercise.
Fuller
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Department of Physiology, University of the Witwatersrand, Medical School, Parktown 2193, Johannesburg, South Africa. 127andy@chiron.wits.ac.za
Carter
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Mitchell
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D000005:Abdomen / Q000502:physiology*; D000818:Animals; D001831:Body Temperature / Q000502:physiology*; D001833:Body Temperature Regulation / Q000502:physiology; D001921:Brain / Q000502:physiology*; D006358:Hot Temperature / Q000009:adverse effects*; D007031:Hypothalamus / Q000502:physiology; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013686:Telemetry